Swiftfox is an optimized build of Mozilla Firefox for AMD processors including Athlon XP, Athlon 64, Duron and Sempron.

That says it all. In my system (Ubuntu Dapper, k7 kernel, AMD Athlon64 3000+) I noticed that the load times are practically eliminated plus the rendering times are down to the middle if I believe this:
http://scragz.com/tech/mozilla/test-rendering-time

If you are on Linux and have an AMD CPU I really suggest you check it out, you just run it and it uses Firefox's bookmarks, extensions etc. You may want to copy the content from your mozilla plugin dir for ...../swiftfox/plugins for them to work.